Calculation of bond dissociation energies for large molecules using locally dense basis sets

A method is given for the calculation of gas-phase bond dissociation energies (BDEs) for relatively large molecules. The method combines the use of locally dense basis sets (LDBS) with density functional theory, using the B3LYP functional. For water and propene, primary and secondary regions are defined and the BDE is tested for consistency with respect to full (primary basis) calculations. Results obtained with LDBS closely approach the limit of using large basis sets throughout. An application of biochemical interest is the determination of the O-H BDE of α-tocopherol, which contains 81 atoms.